Visual field effects in the discrimination of sine-wave gratings

The time needed to decide whether the second of two successively presented sinusoidal gratings was of a higher or lower spatial frequency than the first was measured for spatial frequencies of 1, 2, 4, 8, and 12 cycles per degree (cpd) presented in either the left visual field (LVF) or right visual field (RVF). A LVF advantage was found for discriminating within the low-spatial-frequency range (i.e., 1 and 2 cpd), whereas a RVF advantage was found for discriminating within the high-spatial-frequency range (i.e., 4-12 cpd). These findings support the conclusion that hemispheric asymmetries in the processing of gratings arise when comparisons are made between the output of spatial-frequency channels.     

Haptic roughness perception of linear gratings via bare finger or rigid probe

The magnitude of perceived roughness was haptically estimated as subjects freely explored linear gratings with either the bare finger or a rigid stylus-shaped probe. A considerably expanded range of ridge and groove width was investigated, relative to the extant literature. The four experiments collectively indicate that, for both finger and probe-end effectors, the variance in the estimates of perceived roughness was predominantly predicted by a single parameter: groove width. The functions relating perceived roughness to groove width increased over a narrow band relative to the full range of values, then flattened. These data have archival values for models of roughness perception involving both direct and indirect touch.     

A digital noise and sine-wave generator

A circuit is described that will digitally generate three kinds of signal useful in auditory research: broad-band pseudorandom noise, low-pass-filtered Gaussian noise, and low-distortion sine waves. This digital circuit has two advantages over its analog counterparts, ease of calibration and adaptation to computer control.     

A personal computer programmable sine-wave generator

A programmable sine-wave generator has been developed that permits microcomputer control of both discrete and continuous variations in the frequency and amplitude of auditory, visual, or vibrotactile stimuli. The function and design of the sine-wave generator as a peripheral to the Apple II/FIRST system are detailed. Moreover, adaptations of the basic sine-wave circuit are briefly described for interfacing it with other microcomputers (e.g., the IBM PC and compatibles), and for altering the waveform, range, and resolution of the output. Sample programs in Apple II/FIRST and Applesoft BASIC for controlling signal frequency and amplitude are used to illustrate the simplicity of programmable control. The sine-wave generator has many of the capabilities of commercially available ones, at a fraction of the cost.     

Haptic perception of wetness

In daily life, people interact with textiles of different degrees of wetness, but little is known about the mechanics of wetness perception. This paper describes an experiment with six conditions regarding haptic discrimination of the wetness of fabrics. Three materials were used: cotton wool, sponge-structured viscose and thin viscose. Two ways of touching were investigated: static touching, in which only thermal cues were available, and dynamic touching, in which additional mechanical cues were available. For dynamic touching, average Weber fractions for discrimination were around 0.3, whereas for static touching, they ranged from 0.34 to 0.63. The results show that people can make use of the additional mechanical cues to significantly improve their discrimination performance. There was no significant difference between Weber fractions for the three materials, showing that wetness can be judged as a separate perceptual quantity, independent of the material.     

Haptic pop-out of movable stimuli

When, in visual and haptic search, a target is easily found among distractors, this is called a pop-out effect. The target feature is then believed to be salient, and the search is performed in a parallel way. We investigated this effect with movable stimuli in a haptic search task. The task was to find a movable ball among anchored distractors or the other way round. Results show that reaction times were independent of the number of distractors if the movable ball was the target but increased with the number of items if the anchored ball was the target. Analysis of hand movements revealed a parallel search strategy, shorter movement paths, a higher average movement speed, and a narrower direction distribution with the movable target, as compared with a more detailed search for an anchored target. Taken together, these results show that a movable object pops out between anchored objects and this indicates that movability is a salient object feature. Vibratory signals resulting from the movable ball were found to be a reasonable explanation regarding the sensation responsible for the pop-out of movability.     

Haptic perception of spatial relations

There are some indications that haptic space like visual space is not Euclidean (e.g. Blumenfeld, 1937 Acta Psychologica 2 125-174). In a series of experiments, we investigated the haptic perception of spatial relations in a systematic way. We restricted ourselves to a horizontal plane at waist height. Blindfolded subjects were asked to perform three tasks with their right hand: (i) a reference bar was presented under four different orientations and subjects were asked to rotate a test bar such that it felt to be parallel to the reference bar; (ii) subjects had to rotate two test bars in such a way that they felt collinear; (iii) subjects had to point a test bar in the direction of a marker. Bars and marker could appear at nine different locations. In all experiments large systematic deviations (up to 40 degrees) were made. The deviations strongly correlated with horizontal (right-left) but not with vertical (forward-backward) distance. Subjects showed qualitatively identical trends but the size of the deviations was strongly subject-dependent. In addition, a significant haptic oblique effect was found. These results provide strong evidence that haptic space in non-Euclidean.     

Haptic perception of texture gradients

To pick up 3-D aspects of pictures is arguably the most difficult problem concerning tactile pictorial perception by the blind. The aim of the experiments reported was to examine the potential utility of texture gradients in this context. Since there is no theoretical basis for predicting absolute values of 3-D properties from 2-D patterns read by the finger pads, the abilities of participants to perceive gradients lying between known maxima and minima were assessed. Experiment 1 involved blindfolded sighted participants making verbal magnitude estimations of texture-gradient magnitudes corresponding to plane surfaces at different slants. In experiment 2 the participants' task was to orient a surface at a slant corresponding to the texture gradients depicted tactually, and experiment 3 required early-blind participants to attempt the same task. The results revealed that participants can scale the magnitudes of texture gradients with high precision and that they can also accurately produce surface slants from depictions, providing the extreme conditions are clearly defined and there are opportunities for learning. Texture gradients appear as informative to the blind as they do to the sighted. To what extent these data can be generalised to other gradients and textures or to other projections of 3-D scenes remains to be investigated.     

Haptic perception in newborns

Two experiments using different procedures were performed in which newborns’ ability to process information about object shape with their hands was explored. In the first experiment, a haptic fixed‐trial procedure was used and a decrease in holding times was found for both right and left hands. In the second experiment, discrimination between objects was studied in which a shifted procedure associated to an infant‐control procedure followed by a dishabituation procedure was used. Habituation to an object and a reaction to the novelty of a new object were shown for both right and left hands, showing that neonates are able to process and encode some information about object shape and then to discriminate between different shapes. It is the first evidence of such an ability in neonates. Methodological procedure and haptic cognition with regard to sensory symmetry are discussed and some developmental perspectives are proposed.     

Haptic identification of curved surfaces

In two experiments, the active haptic identification of three-dimensional mathematically welldefined objects is investigated. The objects, quadric surfaces, are defined in terms of the shape index, a quantity describing the shape, and curvedness, a quantity describing overall curvature. Both shape index and curvedness are found to have a significant influence on haptic shape identification . Concave surfaces lead to a larger spread in responses than convex ones. Hyperbolic surfaces show a slight tendency to be identified with more difficulty than elliptic ones. Surfaces with a high curvedness are identified more easily than those with a low curvedness. Results from experiments with constant and with random curvedness are indistinguishable . It is concluded that shape index and curvedness are psychophysically not confounded.     

Haptic face processing.

We present an overview of a new multidisciplinary research program that focuses on haptic processing of human facial identity and facial expressions of emotion. A series of perceptual and neuroscience experiments with live faces and/or rigid three-dimensional facemasks is outlined. To date, several converging methodologies have been adopted: behavioural experimental studies with neurologically intact participants, neuropsychological behavioural research with prosopagnosic individuals, and neuroimaging studies using fMRI techniques. In each case, we have asked what would happen if the hands were substituted for the eyes. We confirm that humans can haptically determine both identity and facial expressions of emotion in facial displays at levels well above chance. Clearly, face processing is a bimodal phenomenon. The processes and representations that underlie such patterns of behaviour are also considered.     

Haptic perception of linear extent

The perception of linear extent in haptic touch appears to be anisotropic, in that haptically perceived extents can depend on the spatial orientation and location of the object and, thus, on the direction of exploratory motion. Experiments 1 and 2 quantified how the haptic perception of linear extent depended on the type of motion (radial or tangential to the body) when subjects explored different stimulus objects (raised lines or solid blocks) varying in length and in relative spatial location. Relatively narrow, shallow, raised lines were judged to be longer, by magnitude estimation, than solid blocks. Consistent with earlier reports, stimuli explored with radial arm motions were judged to be longer than identical stimuli explored with tangential motions; this difference did not depend consistently on the lateral position of the stimulus object, the direction of movement (toward or away from the body), or the distance of the hand from the body but did depend slightly on the angular position of the shoulder. Experiment 3 showed that the radial-tangential effect could be explained by temporal differences in exploratory movements, implying that the apparent anisotropy is not intrinsic to the structure of haptic space.     

Haptic underestimation of angular extent

To what extent can individuals accurately estimate the angle between two surfaces through touch alone, and how does tactile judgment compare to visual judgment? Subjects' ability to estimate angle size for a variety of haptic and visual stimuli was examined in a series of nine experiments. Triangular wooden blocks and raised contour outlines comprising different angles and radii of curvature at the apex were used in experiments 1-4 and it was found that subjects consistently underestimated angular extent relative to visual baselines and that the degree of underestimation was inversely related to the actual size of the angle. Angle estimates also increased with increasing radius of curvature when actual angle size was held constant. In contrast, experiments 5-8 showed that subjects did not underestimate angular extent when asked to perform a haptic-visual match to a computerized visual image; this outcome suggests that visual input may 'recalibrate' the haptic system's internal metric for estimating angle. The basis of this cross-modal interaction was investigated in experiment 9 by varying the nature and extent of visual cues available in haptic estimation tasks. The addition of visual-spatial cues did not significantly reduce the magnitude of haptic underestimation. The experiments as a whole indicate that haptic underestimations of angle occur in a number of different stimulus contexts, but leave open the question of exactly what type of visual information may serve to recalibrate touch in this regard.     

Spatial frequency and the detection of temporal discontinuity in superimposed and adjacent gratings

The properties of the detecting mechanism involved in the resolution of temporal discontinuities of visually presented stimuli have been investigated in two experiments. In Experiment 1, observers made judgments of discontinuity when superimposed presentations of sine-wave gratings of 1, 3, 6, and 10 cycles/deg were presented for either a 20- or a 200-msec duration per presentation at a contrast of .1 and .4. Threshold separation for discontinuity detection indicated a linear increase as spatial frequency increased, with a lesser effect for longer duration exposure and higher contrast. Experiment 2 involved adjacent presentation of the second grating, and a small linear decrease in separation threshold as a function of increasing spatial frequency occurred. The effect of spatial frequency on temporal discontinuity detection is dependent on whether the second stimulus is superimposed or adjacent.     

Haptic tracking permits bimanual independence

This study shows that in a novel task-bimanual haptic tracking-neurologically normal human adults can move their 2 hands independently for extended periods of time with little or no training. Participants lightly touched buttons whose positions were moved either quasi-randomly in the horizontal plane by 1 or 2 human drivers (Experiment 1), in circle and square patterns in the vertical plane by 2 human drivers (Experiment 2), or at different frequencies in the horizontal plane by 2 human drivers (Experiment 3). Bimanual contact was maintained equally well in all conditions even though in Experiment 1 the left- and right-hand motions were uncorrelated (in the 2-driver condition), in Experiment 2 the left- and right-hand motions were spatially incongruous when circles and squares were tracked at the same time, and in Experiment 3 the left- and right-hand motions maintained different frequency ratios. Because haptic tracking has revealed that humans can in fact move their 2 hands independently, it may have potential as a new behavioral tool for revealing other perceptual-motor capabilities.     

Haptic concepts in the blind

We investigated and compared the acquisition of haptic concepts by the blind with the acquisition of haptic concepts by sighted controls. Each subject—blind, sighted but blindfolded, sighted and touching, and sighted only-initially classified eight objects into two categories using a study/test format, followed by a recognition/classification test involving old, new, and prototype forms. Each object varied along the dimensions of shape, size, and texture, with each dimension having five values. The categories were linearly separable in three dimensions, but no single dimension permitted 100% accurate classification. The results revealed that blind subjects learned the categories quickly and comparably with sighted controls. On the classification test, all groups performed equivalently, with the category prototype classified more accurately than the old or new stimuli. The blind subjects differed from the other subjects on the recognition test in two ways: They were least likely to false alarm to novel patterns that belonged to the category but most likely to false alarm to the category prototype, which they falsely called “old” 100% of the time. We discuss these results in terms of current views of categorization.     

Haptic perception of linear extent.

The perception of linear extent in haptic touch appears to be anisotropic, in that haptically perceived extents can depend on the spatial orientation and location of the object and, thus, on the direction of exploratory motion. Experiments 1 and 2 quantified how the haptic perception of linear extent depended on the type of motion (radial or tangential to the body) when subjects explored different stimulus objects (raised lines or solid blocks) varying in length and in relative spatial location. Relatively narrow, shallow, raised lines were judged to be longer, by magnitude estimation, than solid blocks. Consistent with earlier reports, stimuli explored with radial arm motions were judged to be longer than identical stimuli explored with tangential motions; this difference did not depend consistently on the lateral position of the stimulus object, the direction of movement (toward or away from the body), or the distance of the hand from the body but did depend slightly on the angular position of the shoulder. Experiment 3 showed that the radial-tangential effect could be explained by temporal differences in exploratory movements, implying that the apparent anisotropy is not intrinsic to the structure of haptic space.     

Haptic and visual perception of roughness

In this study, we are interested in the following two questions: (1) how does perceived roughness correlate with physical roughness, and (2) how do visually and haptically perceived roughness compare? We used 96 samples of everyday materials, such as wood, paper, glass, sandpaper, ceramics, foams, textiles, etc. The samples were characterized by various different physical roughness measures, all determined from accurately measured roughness profiles. These measures consisted of spectral densities measured at different spatial scales and industrial roughness standards (R(a), R(q) and R(z)). In separate haptic and visual conditions, 12 na?ve subjects were instructed to order the 96 samples according to perceived roughness. The rank orders of both conditions were correlated with the various physical roughness measures. With most physical roughness measures, haptic and visual correspondence with the physical ordering was about equal. With others, haptic correspondence was slightly better. It turned out that different subjects ordered the samples using different criteria; for some subjects the correlation was better with roughness measures that were based on higher spatial frequencies, while others seemed to be paying more attention to the lower spatial frequencies. Also, physical roughness was not found to be the same as perceived roughness.